The present invention relates generally to an electric machine, such as an electric motor, and in particular to the sizing and the shaping of the parts thereof, which are subject to magnetostrictive forces, such as rotor and stator stacks.
Magnetic fields that are present in electrical machines generate forces that are substantially the main function and purpose of such machines. However, these forces also tend to mechanically distort the working parts, that is, the parts that are involved in the operation of the machine. As a consequence, the tangential component of the electromagnetic forces generating the working torque in an electric motor acts on the rotor and stator teeth and distorts them in a tangential direction. The radial component, although usually undesired, is always present and in some cases, such as in variable reluctance motors, reaches quite high values and causes radial distortions. These forces, which are generally variable with time, bring about elastic deformations and, hence, vibrations of the machine. If the natural mechanical-resonance frequencies happen to be present in the vibrations, such vibrations are amplified and the machine can become quite noisy.